Intumescent materials are used for a variety of passive fire protection applications. Such intumescent materials generally comprise a mixture of heat resistant inorganic fibers and an intumescent substance. In use, the intumescent material is applied to a surface to be protected from fire. In the event of a fire, the presence of the intumescent substance causes the intumescent material to expand to form an effective seal against the passage of fire and smoke.
The degree to which the intumescent fire protection material expands is important during a fire event, as the intumescent fire protection material must fill the space it is designed to occupy and must do so at a rapid rate. Accordingly, intumescence at the temperatures commonly encountered in a fire event, rapid rate of expansion, and a high degree of expansion are all desirable performance properties of an intumescent fire protection material. A high degree of expansion ensures that the intumescent fire protection material will expand firmly against the periphery of the opening to be sealed, thereby providing an effective seal against the passage of fire and smoke.
Certain prior art intumescent fire protection materials, such as intumescent gaskets, glazings and pipe wraps, consist of either a graphite-based sheet material or a sodium silicate-based sheet material. Each of these materials has advantages over the other. While expandable graphite possesses a larger expansion ratio at temperatures commonly encountered in a fire, the use of the material is limited by its char strength. On the other hand, the sodium-silicate-based fire protection materials possess higher char strengths, but are limited in use due to their lower expansion ratio at temperatures encountered in a fire.
It is important in fire protections applications that, once the fire protection material has expanded in response to exposure to elevated temperatures during a fire, that the material cannot shrink if maintained at the increased temperature or exposed to repeated heating and cooling thermal cycling. Because of the low char strengths of sodium silicate-based materials, shrinkage occurs in both situations.
Accordingly, it is desirable to provide an intumescent material that possesses high degree of expansion and char strengths for use in passive fire protection applications, which does not exhibit substantial shrinkage upon prolonged exposure to elevated temperatures or thermal cycling.